Border Patrolman Jorge Diaz left Mexico at 12. For 20 years, he's trolled the South Texas brush for illegal compatriots.

Working for the Border Patrol has never been so dangerous. Agents were attacked 987 times along the border during the 12-month period that ended September 30, according to the agency, a 31 percent increase from the 752 attacks recorded the year before and the highest number since the Border Patrol began recording assaults in the late '90s. None of Diaz's agents has been attacked, but it's something against which he is constantly vigilant.

Shortly after passing the Dollar General truck, Diaz picks up Agent Sauceda and heads out to Highway 57, a road smugglers often use to circumvent the patrols on I-35. After about an hour of scanning the road for smugglers but mostly seeing hunters towing dead bucks or locals on their way to visit family, they pull into a gas station and curio shop just off the highway. It's the only building visible amid vast stretches of cabbage fields and open sky.

They're greeted at the door by the owner, a tall Anglo man with a paunch and a thin brown mustache. He has ranches on both sides of the border, he says, and he leases his land to hunters. The drug violence has spooked his clients and affected business. "The more heat they put on the border up here, the more B.S. goes on down there," he says, speaking in a twangy drawl. "I was coming across near Acuña the other day, and I saw just three Border Patrol agents. Anyone could take a load through there." He shakes his head. "They shoulda put in a border security system 20 years ago. Now, it's saturated."

Diaz checks immigrants' documents on Interstate 35 north of Laredo.

Jorge Diaz, a naturalized citizen from a family of migrant farm workers, checks trains north of Laredo for illegal immigrants. He was born in Mexico, but his loyalties to the United States are clear.

Diaz and Sauceda nod sympathetically, and the man continues. "A few years ago, we were down by Acuña, butted up against a fence line, rattling, trying to take down a big buck, and all the sudden here comes some people down the bank with automatic weapons. I said, 'Hell, it's time to crawl outta here.' A few days later, there was a cartel shootout." His ranch homes have been broken into, he says, and three years ago, whoever broke in did $30,000 worth of damage.

He turns and points to the shelves behind him. They're cluttered with Virgen de Guadalupe statuettes, silver jewelry and cow hides. He points out a large statuette in the back that resembles a skeleton. "That's Santa Muerte," he says, referring to La Santisima Muerte, the grim reaper figure that some people beseech for love, luck and protection. "The drug dealers build shrines—I saw one out by Amstel Lake­—and they put those up there to pray that they don't get caught."

On a recent afternoon, while searching for drug loads and unauthorized immigrants sneaking through the brush, Diaz stumbles across something else. He has pulled into the Exxon Mobil for tacos, and when he heads for the lunch counter, he notices a group of Mexican men sitting at a table. He strides over and addresses them in Spanish. "Who of you have immigration papers?"

The six men shake their heads.

"Nadie?" No one?

The heads shake again.

"We're on our way back from Tennessee," one man says. "We're going back home, to Oaxaca."

Diaz smiles and assumes his friendliest, most non-threatening demeanor. "So, you have trucks full of money, then?" he jokes.

The men smile and shake their heads no.

"So, how'd you cross?" Diaz asks.

One of the younger men, in his 20s, says they crossed near Laredo six months ago, went to Nashville to work construction and recently decided to go back to Mexico because there wasn't as much work as they expected.

"You crossed here and you didn't come say hi to me?" Diaz says. "Am I that scary? Am I that ugly?" This time, he gets a laugh from most of the guys. One, though, an older man with gray whiskers and a baseball cap emblazoned with an eagle and an American flag, doesn't look amused. He sits with his arms crossed tightly across his chest, eyeing Diaz suspiciously.

"We just need to take you to the station and process you," Diaz tells them. "We're not going to take money or property or anything like that. Then you can be on your way back home." The men will be fingerprinted and voluntarily deported, and if in the future they come back, they could be prosecuted.

Diaz takes out his handheld radio and calls for backup. He turns to me. "When I saw these guys—maybe it's training—but I knew they didn't have anything," he says. "I don't like these cases. We're supposed to be getting people who are coming in. But if they're illegal, they're illegal." Besides, like many of the people driving south this time of year before the holidays, they may be planning to come back to the United States in January. He addresses the group while he waits for his agents to arrive.

"Tell your friends and cousins that crossing is getting harder," he says. "You can go to jail now, and there are more agents all the time. Spread the word."

I ask if their friends and family in Mexico have heard about the recent crackdown.